E800 is the acronym for Enhanced 800. It is an SS7 service that drives toll free calling. The E800 service covers all numbers in the 800, 888, 877, 866, & 855 area codes. When a person places a toll free call the SSP that serves them initiates a query to an SCP to get the POTS number associated with the toll free number. This query is then routed through the SS7 network to the destination SCP. The SCP does a lookup on the toll free number and returns a response with the POTS number that it represents. A normal ISUP call is then initiated to this POTS number.